Almost as old as the Fischer-Tropsch process for making hydrocarbons is the Fischer-Tropsch process for making alcohols. The reaction is carried out by passing a mixture of carbon monoxide and hydrogen over a catalyst for the hydrogenation of the carbon monoxide. A typical review article is R. B. Anderson et al., Industrial and Engineering Chemistry, Vol. 44, No. 10, pp. 2418-2424. This paper lists a number of catalysts containing zinc, copper, chromium, manganese, thorium, iron occasionally promoted with alkali or other materials for making various alcohols The authors state that ethyl alcohol is a major constituent, the yield of methanol is usually very small and a tentative summary of factors favoring the production of alcohols are high pressure, low temperature, high space velocity, high recycle ratio and carbon monoxide-rich synthesis gas.
Molybdenum is known to be catalytic for the Fischer-Tropsch process and is taught in U.S. Pat. Nos. 4,151,190 and 4,199,522 which are incorporated herein by reference. The references describe some of the herein used catalysts but do not teach that the catalyst is useful for making commercially significant quantities of alcohols.
U.S. Pat. No. 2,490,488 discloses that molybdenum sulfide methanation catalysts acquire Fischer-Tropsch activity when promoted with an alkaline compound of an alkali metal. The example of the invention shows a 30 percent selectivity to C.sub.3 + hydrocarbons and oxygenates. Of this 30 percent, no more than 44 percent boils near or above 65.degree. C. the boiling point of methanol. Accordingly the maximum possible alcohol selectivity is no more than 13.2 percent (44 percent of 30 percent).
U.S. Pat. No. 2,539,414 describes a Fischer-Tropsch process with molybdenum carbide catalysts. It teaches that the catalyst may be used to form oxygenates and at column 3, lines 66-71 teaches that one might get alcohols or hydrocarbons by varying the conditions.
G. T. Morgan et al., J. Soc. Chem. Ind., Vol. 51, 1932 January 8, pp. 1T-7T, describe a process for making alcohols with chromium/manganese oxide catalysts promoted with alkali.
A number of references teach production of alcohols using rhodium catalysts. Some of these contain molybdenum as an optional ingredient. U.S. Pat. No. 4,014,913 discloses a catalyst containing rhodium and thorium or uranium and iron or molybdenum or tungsten for the production of ethanol. U.S. Pat. No. 4,096,164 discloses the use of rhodium in combination with molybdenum or tungsten. Example A discloses that use of a molybdenum-on-silica catalyst yielded 4.4 percent oxygenates.
EPO application No. 81- 33,212 (Chemical Abstracts 96:51,800a) discloses a similar process using rhodium in combination with one or more of a long list of metals which includes molybdenum.
EPO application No. 79-5,492 (Chemical Abstracts 92:166,257b), Hardman et al., discloses the production of alcohols using a 4-component catalyst. The first component is copper, the second is thorium, the third an alkali metal promoter and the fourth a long list of metals one of which is molybdenum. Chemical Abstracts 96:106,913x, Diffenbach et al., disclose a nitrided iron catalyst which is promoted with molybdenum for making alcohols from synthesis gas.
All of the aforementioned references are hereby incorporated by reference.
U.S. patent application Ser. No. 476,674, filed Mar. 18, 1983 and U.S. patent application Ser. No. 622,029, filed June 18, 1984, which are incorporated herein by reference disclose a process for making mixed alcohols by contacting hydrogen and carbon monoxide with a catalyst containing, molybdenum, tungsten or rhenium in combination with an alkali(ne earth) promoter and optionally a support. The Applicants disclose that other metals such as iron, nickel or cobalt may also be combined with their catalyst but do not teach advantageous results for the combination.
While this process is an advance over the art it would be more advantageous if it were possible to decrease the percentage of methanol in the mixed alcohols made. Methanol has been blamed for difficulties when blended into motor gasolines. Accordingly there is some advantage to varying or minimizing the ratio of C.sub.1 to C.sub.2 + alcohols in the mixed alcohols made by the processes of Ser. No. 476,674 and Ser. No. 622,029.
U.S. application, Ser. No. 635,999, filed on even date herewith, which is incorporated herein by reference discloses a method for adjusting the ratio of C.sub.1 to C.sub.2 + alcohols in the processes of Ser. No. 476,674 and Ser. No 622,029 by adjusting the addition rate of a sulfur releasing substance to the H.sub.2 /CO feed. Increasing the sulfur level decreases the C.sub.1 to C.sub.2 + alcohols ratio. Concurrently, however, increasing the sulfur in the feed also decreases the activity or weight of alcohols per unit weight of catalyst per unit of time. It would be more desirable to lower the C.sub.1 to C.sub.2 + ratio without lowering the activity of the catalyst. Use of sulfur releasing substances also requires that sulfur be removed from the mixed alcohols product.
To make a commercially significant alcohol process, one must use a catalyst and conditions which are highly efficient. To be efficient the catalyst must yield a high ratio of mass of product per given mass of catalyst in a given period of time. The catalyst must be stable and active for long periods of time between regenerations. This may be particularly difficult to accomplish when the H.sub.2 /CO ratio of the feed gas is low, such as less than 2 to 1. Ideally the catalyst will be highly selective to a commercial product to avoid purification or removal and disposal of by-products and to avoid separation into two or more product streams.
When the mixed alcohols product is to be used as a fuel replacement or a fuel additive it may be desirable that the ratio of C.sub.1 to C.sub.2 + alcohols be no greater than a certain amount. As used in this Application, the ratio of C.sub.1 to C.sub.2 + alcohols means the weight ratio of methanol to higher alcohols such as ethanol, propanols, butanols, etc., taken as a whole. This number may be calculated by determining the weight fraction of methanol in the mixed alcohols. When the weight fraction of methanol is x, the ratio of C.sub.1 to C.sub.2 + alcohols is x/1-x. Since C.sub.2 + alcohols, in its broadest definition refers to alcohols which are not detected by conventional analytical techniques, a more meaningful approximation of the C.sub.1 to C.sub.2 + ratio of methanol to higher alcohols includes only the C.sub.2 -C.sub.5 alcohols in the definition of C.sub.2 + alcohols. Alcohols bound as esters or ethers are not included in either the C.sub.1 or C.sub.2 + numbers.